1. Field of the Invention
This invention relates to a technique of moving liquid in a flow path to thereby form a flow.
2. Related Background Art
Pumps of various types are known as means for moving liquid. They are divided broadly into non-volume type pumps and volume type pumps by the basic principle and mechanism. The non-volume type pumps include centrifugal pumps, mixed flow pumps, axial flow pumps, friction pumps, etc. The volume type pumps include reciprocating pumps, rotary pumps, etc.
The reciprocating pumps are often used to feed a relatively slight quantity of liquid. The reciprocating pumps include recipro-type pumps and syringe-type pumps. The recipro-type pump is a pump in which a plunger is reciprocated at a high speed in a syringe and liquid is fed by the differential between an inlet valve and a discharge valve, and the syringe-type pump is a pump in which liquid is inhaled into a syringe and a plunger is moved to discharge and feed the liquid. These pumps are capable of even feeding liquid at a slight flow rate of the order of 10 .mu.l/min.
These conventional pumps, however, are bulky and have suffered from the problem that dead space in the cylinder of the pump is unavoidable and a great deal of liquid including the volume of liquid in the cylinder becomes necessary as a whole quantity of liquid.
In order to eliminate this problem, an apparatus as a micropump which can feed a slight quantity of liquid is proposed in a U.S. patent application Ser. No. 07/979,811 filed on Nov. 20, 1992. This apparatus is such that a resistance heat generating element or a piezoelectric element is provided in a minute tubular flow path and a short pulse-like voltage is applied thereto, whereby a slight quantity of fluid is discharged outwardly as a droplet by the impact force of a volume change caused by a bubble momentarily created by the heating of the resistance heat generating element or a momentary volume change caused by the electrostriction of the piezo-electric element, and the pulse voltage is repetitively imparted to repeat the discharge of a droplet for each pulse and thereby form a flow in the flow path.
This micropump is very compact and is an excellent system which has no dead space like a cylinder and can therefore feed a slight quantity of liquid accurately.